Non-flammable deep eutectic based polymer electrolytes for lithium metal batteries

Deep eutectic solvent (DES) electrolyte, due to its low volatility, flame retardancy and environmental friendliness, has become one of the next-generation electrolytes for lithium metal batteries (LMBs). However, DES has poor compatibility with lithium metal and there is still a risk of leakage, which limits the use of DES in LMBs. The introduction of polymers into the electrolyte is an effective strategy to solve the leakage problem and improve the compatibility of the interface. Here, we report a polymer formed from nitrogen-rich monomers that polymerize in-situ in the flame-retardant DES (1 mol/L LiTFSI in succinonitrile) to form a gel electrolyte (D-TAEA). D-TAEA maintains high ionic conductivity (0.52 mS cm −1 at 30 °C) while effectively inhibiting electrolyte leakage and optimizing interface stability. Benefiting from the synergistic effect of polyurea and tertiary amine groups, D-TAEA exhibits a wide electrochemical window (5.0 V vs Li/Li + ), high Li + migration number (0.69) and excellent cycle performance. Due to the stable SEI formed by D-TAEA and Li electrode, Li/Li symmetrical battery can stably cycle for 800 h, moreover, the capacity retention rate of LiFePO 4 full battery remains at 92.6 % after 300 cycles at 0.1C. Therefore, this three-dimensional cross-linking network provides a new path for the traditional DES system.